The present invention relates to internal gear pumps including an outer rotor and an inner rotor eccentrically engaged therewith.
As to internal gear pumps including an outer rotor having an internal gear portion on the inner periphery and an inner rotor having an external gear portion on the outer periphery and eccentrically engaged with the internal gear portion of the outer rotor, a reduction in leakage of hydraulic fluid through a slight clearance between a side of each rotor and a pump housing is an essential factor for improving the pump efficiency. Such leakage reduction is achieved by means of a structural contrivance shown, e.g. in JP-U 4-125687 or JP-A 7-102928.
JP-U 4-125687 discloses an internal oil pump including an outer rotor having an outer periphery rotatably held by rotor holding members screwed to a pump housing and an inner rotor held by a side plate formed with the outer rotor and the pump housing.
JP-A 7-102928 discloses an oil pump including outer and inner rotors accommodated in an oil-pump casing and held by the oil-pump casing and a rotary cover screwed thereto.
As to the internal oil pump disclosed in JP-U 4-125687, however, a plurality of rotor holding members need is to separately be disposed along the outer periphery of the outer rotor, requiring a lot of time for their assembling and adjusting.
As to the oil pump disclosed in JP-A 7-102928, singe the structure that the rotary cover is in slide contact with either side of each outer rotor and inner rotor involves greater friction, the rotary cover needs to be subjected to lightening working for friction reduction, resulting in the increased number of working processes.
It is, therefore, an object of the present invention to provide internal gear pumps with the reduced number of parts and working processes and smaller friction.